Hi, thanks for the report, and sorry for the trouble!
To be upfront: the current converter doesn't support transparent (alpha) materials — any part of a model that's meant to be see-through (like glasses lenses) will currently render as solid/opaque instead. That's a known limitation on our side, not something wrong with your avatar or how you converted it.
As a workaround, you can use the Lab feature's "Delete Mesh" tool (open the tool's main window -> Lab -> Delete Mesh) to remove fully-transparent meshes such as glasses lenses from the conversion entirely, so they don't show up as opaque blocks.
For the texture issue, we'd need a diagnostic log to tell whether it's on our side or specific to your model — could you submit a report through the in-app "Inquiry" (問い合わせ) form after a conversion attempt? It automatically attaches the log, which helps us pinpoint the cause much faster than a description alone.
We're looking into proper transparency support, though we can't promise a timeline yet. Thanks again for your patience!